DESCRIPTION: Duplication of the maternally-derived copy of the imprinted region on chromosome 15q is associated with a major risk for autism or autism spectrum disorders. The duplications arise by homologous but unequal recombination through series of transcribed repeats in the region and variation in the alignment at crossing over lead to difference in the content and origin of the chromatin involved. The investigator?s goals are directed toward understanding the role that duplication of chromosome 15q plays in autism by examining the phenotypic sequelae in probands with known duplications. She also proposes to define the autism critical region by detailed examination of rearrangements in probands with unusual breakpoints or imprinting errors.